Determination of Germanium in Oxides, Ores, and Alloys by Chlorination and Gas Chromatography Basil Iatridis and George Parlssakis" Inorganic and Analytical Chemistry Depadment, National Technical University of Athens, Athens, Greece
A procedure is described for the quantitative determinatlon of germanium In oxldes, ores, and alloys by gas chromatography. The germanium-bearing materlal and carbon tetrachloride are introduced into a glass tube. After both ends of the tube are sealed, the chlorination reaction takes place at an elevated temperature. The volatile products formed, after crushlng of the glass capsule, are analyzed by gas chromatography. The proposed method has relative accuracy and preclslon better than -4.6% and 0.88%, respectively. I t is applicable to a germanlum level of 1 to 99 % I t Is also rapid, since two samples per hour can be analyzed, and sensltive, g of Ge can be detected. since an amount of
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Germanium, an element of technolqgical importance, is found in a number of natural deposits and is used as a constituent in several alloys in a wide range of percentages. At the present time, procedures for a rapid, simple, sensitive and selective quantitative determination for germanium present several problems (e.g., sample in aqueous phase, use of expensive instrumentation, interference of other elements, and concentration dependence). The aim of the present paper is to propose a method in which many of these disadvantages of existing methods are eliminated. This method is based on the chlorination of Ge-bearing compounds with carbon tetrachloride (CC14)within a small glass capsule, and the subsequent quantitative determination by gas-liquid chromatography of the resulting germanium tetrachloride (GeC14). T h e gas chromatographic behavior and characteristics of germanium tetrachloride which are referred to by a number of papers (1-3) have been used. Several attempts toward a quantitative gas chromatographic determination of germanium as the hydride have been made by G. G. Devyatykh et al. ( 4 ) ,M. Fiser (5), and R. D. Kadeg and G. D. Christian (6). A gas chromatographic determination of germanium in coal has been reported by M. L. Sazonov et al. (7). According t o this method, after a preliminary treatment the sample is chlorinated with hydrogen chloride and the germanium tetrachloride formed is absorbed and concentrated on active carbon and is then submitted to analysis. Qualitative information on the chlorination reaction of germanium oxide with carbon tetrachloride has been reported by Hecht, Jander, and Schlapmann (8). The so-far-successful results obtained (9-1 1 ) by using CC14as the chlorinating agent encouraged its use in the present case for the determination of germanium. The method has been successfully applied to a variety of Ge compounds where germanium is present in a wide concentration range. For the introduction of samples (glass capsules containing the chlorination products) into the gas chromatographic system, a special crushing device (9) is used. This device adapted to the gas chromatographic system is the sample introduction device.
EXPERIMENTAL Reagents and Materials. GeC14. Germanium tetrachloride used for the preparation of the calibration curves was obtained
Table I. Quantitative Determination of Germanium(IV ) Oxide When Compared against Syringe-Injected GeC1, Standards Weighed, Found, Relative mg mg Error % error 3.28 3.25 -0.03 -0.90 2.70 -0.03 -1.10 2.73 2.88 2.86 -0.02 -0.70 4.36 4.34 -0.02 -0.46 1.96 1.94 -0.02 -1.02 2.79 2.80 + 0.01 +0.36 3.93 3.94 +0.01 +0.25 2.72 2.75 + 0.03 +1.10 2.45 2.42 -0.03 -1.20 4.19 4.18 -0.01 -0.24 Average: -0.6 Standard deviation 0.7 from commercial sources (Alfa Ventron, U.S.A). It was purified by isothermal distillation and was kept under absolutely anhydrous conditions. GeOz. Germanium oxide AR was obtained from Alfa Ventron, U.S.A. Germanite Ore. Chemical analysis (by wet chemical and instrumental methods) and x-ray diffraction measurements of germanite ore gave the following results (wt %): Ge = 7.77 0.01, Fe = 23.61 f 0.05, S = 22.97 A 0.01, Cu = 40.20 f 0.04, Ca = 1.17 0.01, SiOn = 1.78 A 0.05, Cu3(Ge,Fe)S4,Cu3FeS4,CuzGeSz, FeGe03, CuFeSz, CuFeS, CuS, Cu2S, FeSz, and SiOz. Ge-Au Alloy. Chemical analysis of the components of the tested alloy gave the following results (wt %): Ge = 12.00 & 0.02, Au = balance. The technique and conditions of preparation, chlorination, and chromatographic determination of the sample tested are described below and constitute the proposed analytical procedure for the quantitative determination of germanium in some typical cases. Sample Preparation and Chlorination Technique-Gas Chromatographic Determination. A borosilicate tube 4 cm long, 6-mm o,d., and 4-mm i.d., sealed at one end, cleaned and dried at 130 "C is used as a reaction tube. To carry out a preparation, a weighed amount of the sample (Tables I, 11) to be analyzed in small pieces (for alloys) or in powdered form (440-600 mesh, for oxides and ores), and dried at 140 "C, is introduced. After this, the open end of the tube is closed with adhesive tape and dry Nz is blown around this part. The lower part of the tube, which is held an a vertical position, is placed in a container of dry ice and the corresponding amount of dry carbon tetrachloride (Table 111) is then added. The tape is removed, the open end sealed, and the capsule withdrawn from the cold bath. Then it is placed in an oven at 575 "C for a given time (Table 111)necessary for the quantitative chlorination of the sample, before placing it in the special crushing device (9). The capsule is broken by the plunger of the crushing device, and the liberated volatile compounds are then swept into the gas chromatographic system by the carrier gas. Calibration Graphs. To obtain the necessary calibration graphs, known amounts of germanium tetrachloride are introduced by a 701N Hamilton syringe into the gas chromatographicsystem. It is essential, after each use, to wash the syringe immediately and carefully. This is done by immersing the lower part of the needle in acetone and simultaneously adding acetone dropwise at the entrance of the plunger. The syringe, after being washed
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Table 11. Determination of Germanium in Ge-Containing Materials Ge% (wt) Relative % Std dev Error i 0.88 -0.25
No. of
Sample Germanite Ge-Au alloy
Weight, mg 7.5-16.5 13.0-20.0
determinations 7 8
Present 7.77 12.00
Found 7.75 11.45
k0.16
-4.6
Table 111. Chlorination and Gas Chromatographic Conditions of Various Germanium Samples Chromatographic conditions CCl, Temperature "C added, Chlorination pL/mg time, min, Crushing Inj . Sample of sample at 575 "C device port Column Det. 110 80 100 1.85 15 120 GeO, 150 80 100 Germanite 1.10 30 150 110 80 100 0.16 15 120 Ge-Au alloy with acetone, is then washed with ether and dried under vacuum. The syringe treated this way can be used for hundreds of injections. Instrumentation. Crushing Device. The crushing device used is the sample introduction device and through it the carrier gas enters the gas chromatographicsystem. It accepts sample holders of various types and sizes. Aside from that, it can be used for gases, liquids, solids, and in general for samples consisting of heterogeneous systems. Likewise, it is possible to serve itself as a microreactor. Apparatus Used. As column packing material, silicon oil DC 550 20% w/w on celite 545 was used because of its inertness toward GeC14and its very good resolution for a number of chlorine compounds (12). A Hewlett-Packard700 G.C. equipped with TCD (Gow-Mac4 tungsten filaments) was used, modified by us in order to keep the oven temperature constant within fO.l "C. Nitrogen was used as carrier gas. This was dried by passing through activated molecular sieve and Pz05traps at flow rates of 10-100 mL/min. The detector used showed a satisfactory response toward inorganic chlorides. From time to time the detector was washed with acetone-hydrochloric acid solution in order to prevent alteration of response owing to deposit of hydrolysis or reaction products upon the filaments. To avoid reaction with the highly corrosive chlorides, glass columns were used (4-mm i.d., 6-mm o.d., 183 cm long). These columns were packed under anhydrous vacuum conditions by inserting glass wool at one end of the column, applying vacuum to that end, and adding the packing material from the other one. The column was vibrated and the vacuum continued until the packing material did not settle any further. Columns were conditioned overnight at the maximum permitted temperature. The effluent end of the column was not connected to the detector during the conditioning period. Column oven temperatures used were at most 30 "C below the maximum recommended temperature limit for isothermal conditions. The chlorinating and chromatographic conditions are shown in Table 111. RESULTS AND DISCUSSION The optimum conditions for the quantitative chlorination of germanium in Ge-containing compounds were determined by a study of the conversion efficiency as a function of time and temperature. Figure 1represents a chromatogram of the reaction products of carbon tetrachloride with germanium(1V) oxide in the glass capsule. The first and second peaks are due to carbon dioxide and phosgene. The third peak is due to germanium tetrachloride, and the last one is attributed to the excess of carbon tetrachloride. In longer time and under higher detector sensitivity, the hexachlorethane peak might be detected depending on CzCl,j quantity. Figure 2 is a typical chromatogram of the reaction of carbon tetrachloride with germanite ore. Generally speaking, this 910
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Carrier gas, mL/min 14
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Figure 1. Gas-liquid chromatogram of chlorination of germanite ore with CCI, (6 min, 575 OC). Chromatographic conditions: glass column length = 183 cm, 0.d. = 6 mm, i.d. = 4 mm. Packing material: silicon oil DC 550 20% w/w on celie 545. Carrier gas flow rate: 14 mL/min N,. Detector: TCD (Gow-Mac 4 tungsten fllaments), bridge current 150 mA. Temperatures "C: capsule chamber, 120; inj. port, 110; column, 80; detector, 100
figure is similar to the previous one. However, two other peaks could be observed: one due to chlorine, which partially overlaps the carbon dioxide peak, and the second due to carbon disulfide. Both these by-products are formed when sulfur is a constituent of the compound to be chlorinated. The chromatogram of the chlorination reaction of carbon tetrachloride with Ge-Au alloy in the glass capsule consists of only two peaks, namely, a germanium tetrachloride and a carbon tetrachloride peak. Under the applied chromatographic conditions, the chlorine peak does not appear because of its small quantity. Carbon dioxide, phosgene, and chlorine in all the abovementioned chromatograms are identified by taking their infrared spectra from collected fractions a t the outlet of the chromatographic column. A comparison of the retention times with those of authentic samples was used for the identification of carbon disulfide, carbon tetrachloride, and germanium tetrachloride peaks. Carbon tetrachloride was chosen as the most appropriate chlorinating agent because of its reducing and chlorinating behavior on oxygen- and sulfur-containing compounds and also for ita inertness toward both the packing material of the
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Flgure 2. Gas-liquid chromatogram of chlorination of Germanium oxide with CCI4 (6 min, 575 "C). Chromatographic conditions: glass column length = 183 cm, 0.d. = 6 mm, id. = 4 mm. Packing material: silicon oil DC 550 20% w/w on celite 545. Carrier gas flow rate: 14 mL/min NP. Detector: TCD (Gow-Mac 4 tungsten filaments), bridge current 150 mA. Temperatures "C: capsule chamber, 150; inj. port, 150; column, 80; detector, 100
column and the entire gas chromatographic system. From the obtained chromatograms and reference (8) it is clear that a number of by-products are formed. Some of them (COZ, COC12, CS2,CL2, C) are due to the reaction of the chlorinating agent with oxygen- and sulfur-containing compounds and result from the thermal alloys, while others (CZCl6,c&&) decomposition of CCll with predominance of the hexachloroethane (13). However, this fact does not affect the quantitative determination of the germanium tetrachloride peak under the applied gas chromatographic conditions. The GeCl, peak area is measured through the trapezoid construction, and the calibration graphs used are linear within the range of 0.2 to 5 mg of Ge. The detector sensitivity (applying a filament current of 150 mA) throughout the determinations was within the range of 200 to 600 mV.mL/mg, and the baseline drift during a single
run as well as during 24 h of continuous operations was negligible (less than 0.01 mV for 1-mV full-scale deflection of the recorder). As is deduced from the obtained results (Tables I, 11), conversion of Ge to its volatile tetrachloride by reaction with CCl, carried out at 575 "C inside a sealed glass tube (microreactor) is quantitative. The proposed method is accurate and precise (relative error
